Effective Antifogging Coating from Hydrophilic/Hydrophobic Polymer Heteronetwork

Abstract Fogging on optical devices may severely impair vision, resulting in unacceptable adverse consequences. Hydrophilic coatings can prevent surface fogging by instantly facilitating pseudo‐film water condensation but suffer from short antifogging duration due to water film thickening with further condensation. Here, an innovative strategy is reported to achieve longer antifogging duration via thickening the robust bonded hydrophilic/hydrophobic polymer heteronetwork coating to enhance its water absorption capacity. The combination of strong interfacial adhesion and hydrophilic/hydrophobic heteronetwork structure is key to this approach, which avoids interfacial failure and swelling‐induced wrinkles under typical fogging conditions. The developed antifogging coating exhibits prolonged antifogging durations over a wide temperature range for repetitious usages. Eyeglasses coated with this coating successfully maintained fog‐free vision in two typical scenarios. Besides, the coating recipes developed in this study also have potential as underwater glues as they demonstrate strong adhesions to both glass and polymer substrates in wet conditions.

immersed in a mixture solution with 90 ml ethanol, 10 ml water, 5 ml 3-glycidoxypropyltrimethoxysilane and 100 μl acetic acid at room temperature for 12 h. After thorough cleaning, the epoxy-functionalized glass slides were prepared. PVA with the mass of 3.6 g was dissolved in 15 ml water (pH = 2) and stirred for 2 h at 95℃. [1,2] After defoaming, the resultant solution was spread on the epoxy-functionalized glass slides to produce a uniform liquid layer with different thickness (25, 100, 200 μm) using a wet film coater. The samples were placed in 60℃ oven for 12 hours to complete chemical grafting of PVA. To obtained dry PVA-SI coated substrates, the samples were dried at 25℃ for 24 h.
Measurement of anti-fogging performance. The anti-fogging performance was characterized by a hot-vapor testing. Concretely, the samples were held above a water bath containing water with constant temperature, and the distance between the samples and the surface of the water was 5 cm. To investigate the anti-fogging properties of the samples, the light transmission over the 300-800 nm wavelength range was collected using a UV-Vis spectrophotometer during fogging tests. For comprehensive evaluation and direct comparison, the average transmission over the 400-800 nm wavelength was defined and obtained from the following equation: The repeated anti-fogging tests were carried on a 60℃ water bath. The sample was first exposed to hot water vapor (60℃) for 10 min (denoted as the wet-state). After a drying process at 25℃ for 12 h (denoted as the dry-state), the second anti-fogging test 3 was carried, etc.
Measurement of volume and mass swelling ratio. The diameter, height and mass of the dry PVA/PTPM film was firstly measured as d 0 , h 0 and m 0 , and then immersed into water at 20℃. After reaching equilibrium swelling, the swollen PVA/PTPM film was taken out, and the diameter and height were measured again as d w , h w and m w .
The volume and mass swelling ratio denoted as Q V and Q M was obtained from the following equations: Measurement of water contact angles. The water contact angles were measured using a contact angle meter (OCA25, Germany).

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR).
ATR-FTIR spectra were collected in wavenumber range of 4000-400 cm -1 on a Bruker Shore hardness test. The shore durometer was placed on the sample and tested by pressing.
Scratching test. The PVA/PTPM HN coatings at dry and wet states were repeatedly scratched using a piece of 500 g weight wrapped with a spectacle cloth. The transmittance of PVA/PTPM HN coatings was measured after 50 cycles of dynamic scratching.

Supplemental Movie
The movie showed the superb anti-fogging performance of the PVA/PTPM HN coated glass slide compared with the pristine one. When exposed to hot water vapor (60℃), the glass with PVA/PTPM HN coating maintained clear visions after 300 s, while the pristine glass slide showed blurred visions at 10 s.

Supplemental Figures
6 Figure S1. The water contact angle of the PVA/PTPM HN coating and bare glass over time.